Expander graphs: Analyzing graphs using spectral techniques has a long history [1]}, [2]}. The main idea behind these approaches is to consider information about the spectrum of a matrix representation of the graph (mainly, the adjacency matrix or the Laplacian). It has been presented by several researchers [3]}, [4]}, [5]} that expansion properties of the graph provide crucial signals in understanding the degree of cohesion in the underlying subgraph structure. High expansion property results in being simultaneously sparse and tightly connected. A graph with such non-trivial structural property are called expander graphs and a comprehensive review on this topic can be found in [6]}
